The present invention relates to metal-oxide-semiconductor (MOS) devices and, more particularly, to a novel MOS-pilot structure for providing a pilot current which is an accurate representation of the total current then flowing in an insulated gate transistor (IGT).
The total current flowing in an operational IGT consists of two components' the MOS channel current and the bipolar current. The MOS channel current flows in response to a voltage being applied to the gate of the IGT, and the bipolar current is the current which is conducted by the bipolar transistor formed by the lower three semiconductor layers of the IGT when a voltage is also applied to the anode of the IGT.
A known prior art IGT pilot structure that allows sensing of the bipolar current has a base region contact connected to ground through a sense resistor This bipolar pilot is undesirably subject to inaccuracies because the bipolar current may not linearly track the main IGT current due to fluctuations in the gain of the bipolar transistor and because of the recombination of the electrons and holes in the drift region of the IGT substrate due to the lifetime of the majority and minority current carriers. Additionally, during turn-off the bipolar current can develop an undesirably large potential difference across the sense resistor between the IGT's base region and ground relative to the cathode of the main IGT cell and ground which can cause avalanche breakdown of the main IGT cell.
Another IGT pilot structure allows the combined MOS channel current and the bipolar current to be sensed. This MOS-pilot structure has a common contact electrical/ connected to both the emitter region and the base region of the IGT and also through a sense resistor to ground. This pilot structure will more accurately track the main IGT current but can also develop the undesirably large potential difference across the sense resistor during turn-off, which can cause avalanche breakdown of the IGT.
It is accordingly a primary object of the present invention to provide a novel IGT MOS-pilot structure which is not subject to the foregoing disadvantages.
It is another object of the present invention to provide a novel MOS-pilot for an IGT which is simple in construction and inexpensive to manufacture.
A further object of the present invention is to provide a MOS-pilot for a multiplicity of IGT cell interconnected in a lattice structure by modifying the lattice structure.
These and other objects of the invention, together with the features and advantages thereof, will become apparent from the following detailed specification when read with the accompanying drawings in which like reference numerals refer to like elements.